Just to follow up on
@CrackPot. Think of the 14 3/8 in shockwave as a pistol that is not on the MA approved firearms roster. If you can get oneit is legal to own it in MAbut (ignoring frame transfers since they don’t apply to the Shockwave) there is no FFL in or out of state who will transfer one to you. Out of state it will have to go to an in state FFL (since it isn’t a long gun) and in state no FFL can transfer it since it isn’t on the approved firearms roster. If an individual sold you one out of statethey would be breaking Federal law since it is considered a “firearm”not a rifle or shotgun (in other wordsthe same as a pistol)so it must go through a FFL in the buyer’s state of residence.
Alsojust like an off roster pistolif you have dual state residency or acquired it while living out of state you can bring it back to MA and register it (note: if you are actually moving into MA from out of state you don’t need to “register" any of your guns).